Peripheral vascular disease (PVD) is a chronic disease that afflicts a relatively large fraction of our elderly population. The level of oxygenation of limb muscles is believed to be an important parameter for the diagnosis of PVD. Angiography of the extremities provides anatomical details of blood flow, but limited information on the level of tissue oxygenation. Other non-invasive methods, including laser Doppler, are relatively superficial and do not directly provide the level of tissue oxygen saturation. We have developed a new technology that can provide specific information on the level of oxygen saturation in tissues based on near-ir frequency domain spectroscopy. The optical signal derives from deep penetration of photon density waves in tissue. Recent advances in our laboratory have elucidated the physical modalities of light diffusion in tissues and have allowed, for the first time, the design and construction of non-invasive portable, relatively inexpensive (about $l0K) monitors of tissue oxygen saturation. We have demonstrated that the method is absolute, quantitative, and accurate in model systems. Preliminary tests with our collaborators at the Dallas VA Medical Center on PVD patients have provided evidence that the optical oxygen monitor can be clinically useful. This project aims at the design and engineering refinement of a monitor of hemoglobin saturation for the diagnosis of PVD. Specifically, we plan to validate the method, to assess the reproducibility and accuracy of the measurement in optically heterogeneous realistic phantoms. In conjunction with our studies, the redesigned optical saturation monitor will be tested by the Dallas clinical team on PVD patients. The result of our research should be the design and characterization of an innovative, non-invasive clinical instrument that will provide the clinician with the physiological parameter that is considered to be the meaningful index for the early detection and treatment of PVD.